The present invention relates generally to electrophotographic machines and to methods of using such machines. More particularly, the present invention relates to a fuser assembly in an electrophotographic machine.
A fuser assembly is used in an electrophotographic machine to fuse previously applied toner onto the surface of a print or copy medium, such as paper. A fuser assembly typically comprises a fuser roller in association with a pressure roller which work together to press the toner onto the print medium. As used herein, the word xe2x80x9cprintxe2x80x9d and the various forms thereof are intended to include printing, copying, and any other form of electrophotographic image production (be it production of an image, text, or otherwise). No limitation is intended by or should be read into the use of the word print. The fuser roller is typically heated to increase the toner""s adherence to the print medium. One method of achieving this result is to use toner with some meltable material such as a plastic so that when heated, the toner effectively melts onto and adheres to the print medium. A variety of methods are known to heat the fuser roller, including heating internally using a heating element, such as a fuser lamp.
Typically, the print medium is rolled between a fuser roller and another roller to ensure proper contact between the fuser roller and the print medium. Proper printing requires that the toner and print medium will reach a certain temperature to facilitate proper binding or adherence of the toner to the print medium. The temperature reached is a product of a variety of factors, including the initial temperature of the fuser roller, the type of print medium employed (e.g., thin paper, cardstock, cardboard, or transparencies), the time the print medium is in contact with the fuser roller, and the heat capacitance of the fuser roller. Where the heat capacitance of the fuser roller is relatively low, or the heat absorbance of the print medium is relatively high, a faser assembly often needs to operate more slowly to ensure proper fusing of toner to the print medium.
The increasing speed and function of electrophotographic printers and copiers has led to a decrease in the contact time between the print medium and the fuser roller. A prior solution to ensure that the print medium and toner reached sufficient temperature was to slow down the throughput of print medium through the printer or copier in order to increase the overall contact time between the print medium and the fuser roller. Throughput references the total amount of printing accomplished within a given time frame. This solution of slowing down the printer has become unacceptable given the present desire for high throughput and accurate printing.
Typically, most fuser rollers operate at one temperature. While this temperature may be suitable for one print medium while the printer is operating at a given speed, it often fails to provide the level of flexibility that might otherwise be provided or that is desired to suit a variety of printing functions. It is desirable to print on a variety of different medium, i.e., medium of different thicknesses and compositions. In many instances printing on thicker-than-normal medium gives rise to a need to adjust the fuser roller temperature and/or the printer throughput in order to sufficiently heat the thicker medium to ensure that the toner adheres to the medium properly. The same is true with printing on transparencies or other materials with varying heat capacitance.
In one embodiment, a device for improved printing is provided. By operating two or more fusing apparatuses within the same image producing cycle, toner is more likely to be properly and adequately fused to print medium. Preferably, this improvement in fusing does not affect the operating speed of an image producing apparatus. This is achieved since the total time a given piece of print medium is in contact with a fuser assembly or otherwise being operated upon by a fuser assembly is at least doubled, by using at least two fusing devices. In accordance with one aspect, the present invention may help to ensure that fusing is not a rate limiting step to the overall throughput in an electrophotographic process.
In accordance with another aspect, the present invention relates to a device for forming images on at least one sheet of medium. The device includes an image forming section for forming an image on the sheet of medium, an output section located substantially downstream of the image forming section. The output section may or may not include a secondary fusing device. Where a secondary fusing device is included, it may be such that it is selectively used by the imaging forming section as needed. Alternatively, the device may include an image forming section, as well as a first fuser and a second fuser to bind toner on a sheet of media. The fusing devices are typically comprised of a plurality of rollers and a motor.
In yet another embodiment of the invention, a method of electrophotographic printing is disclosed. Preferably, the method includes the steps of fusing an image to a print medium with a first fuser and fusing the image to the print medium with a second fuser. Alternatively the method may include steps of determining whether the second fusing step is desired, and determining the temperature of the second fuser.
Additional advantages and novel features of the present invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be appreciated further by practice of the invention.